PROJECT SUMMARY AND ABSTRACT In China, there has been a continuous and persistent rise in the number of reported HIV cases among MSM. The Chinese government has recently demonstrated a strong political will to scale up evidence-based HIV programs and to implement innovative biomedical interventions to control HIV transmission in China. The Chinese Centers for Disease Control and Prevention (CDC) is expected to commence a national pre-exposure prophylaxis (PrEP) initiative during the next few years. In light of the evolving science of PrEP, including potential new modes of PrEP delivery and repeated findings on low PrEP uptake among key populations, there is urgent need to build a strong scientific foundation about strategies to maximize PrEP's future implementation with MSM in China. We will apply a mixed-methods approach using both qualitative and quantitative methods. Our fieldwork will be undertaken in Nanjing, China. The proposed research study linearly extends our past and ongoing MSM HIV research in China. We will collect two-mode affiliation network data with 300 MSM (Phase 1). Based on the results of two-mode affiliation network analysis, we will identify individual MSM and stakeholders from physical and/or virtual spaces who hold network structurally central positions for qualitative in-depth interviews to assess implementation barriers and facilitators for PrEP (Phase 2). Findings will directly inform PrEP implementation policy and research at both the local and national levels in China. The nation's future PrEP promotion program could increase its impact by targeting the structurally central places where risk- taking MSM frequent. Furthermore, we will use findings to support a subsequent application for a larger-scale trial to test the effectiveness of a tailored implementation strategy to deliver PrEP to HIV negative, high-risk MSM (including examining different PrEP delivery modalities such as pill, transdermal and injectable formulations). Findings from this proposed research will provide important groundwork to inform future PrEP implementation in China and may also help create responses to the escalating HIV epidemics among MSM in a wide range of countries.